The present invention relates to a braking device in an arrangement for linear movement, comprising an elongated part and a part that is movable in relation thereto.
In pressurized fluid cylinders, operating with compressible media, such as compressed air, there are great difficulties in braking and keeping the piston--piston rod--straight in one or more pre-determined positions along the stroke of the piston. The piston must be stopped in the intended position and kept in this position, irrespective of whether it is unloaded or loaded. One solution for stopping and fixing the piston in an intended stationary position is to provide the piston--piston rod--with an accompanying belt or chain, which is directly actuable by a braking means. However, there is in this solution great risk of wear and rupture of the belt or chain. Careful maintenance is necessary, as well as smooth braking, if the arrangement is to function properly.
Another solution is illustrated in the European Patent Publication 0104364. This relates to a braking device associated with working cylinder which has no piston rod. A fluid driven braking means is incorporated in the movable dog of the arrangement, the braking means acting against the working cylinder. This means a relatively complicated structure for the fluid driven braking means, as well as the requirement of a flexible line for the fluid supply to the braking means, which moves together with the dog.
There are also great difficulties in achieving effective braking and locking of the dog or rider in cylinders with magnetic pistons, which drive such a rider situated outside the cylinder and guided by it. There is also a corresponding situation for so-called linear motors, where a movable body is moved with the aid of electromagnets along a linear rail or the like.